1. Field of the Invention
The present invention relates to the fabrication of self-aligned contacts on semiconductor devices, and more particularly to a method for making self-aligned source/drain contacts on semiconductor devices using a hard mask.
2. Description of the Related Arts
Because the trend of semiconductor manufacturing is toward highly integrated semiconductor devises, the tolerance of the patterning has become stricter. A self-aligned contact which partially overlays the source/drain and the gate electrode is developed to increase the tolerance of mis-patterning and enhance the density of the integrated devises.
Conventional self-aligned contacts are typically fabricated by the following procedures. Referring to FIG. 1A, a gate oxide layer 112, a gate electrode structure 117 consisting of a gate electrode 114 and a gate protecting layer 116, a lightly doped region 118, a insulating sidewall spacer 120 on the sidewalls of gate electrode structure 117, and a heavily doped region 122 are successively fabricated on a semiconductor substrate 110. Then, an insulating layer 124 is depositing to blanket the substrate 110 and a photoresist 126 is formed on the insulating layer 124.
Turning to FIG. 1B, the conventional self-aligned contact 128 is completed by etching the insulating layer 124 to the gate electrode protecting layer 116 using the photoresist 126 as the mask, and then etching the insulating layer 124 to the heavily doped region using the gate electrode structure 117 and the sidewall spacers 120 together as the mask.
Unfortunately, several problems occurs because of the usage of photoresist as a mask. Photoresist, which is for the most part composed of organic compounds, generates by-products, such as organic polymers in the self-aligned contacts during the etching procedures. That leads to impairment of the devises or the need for additional procedures to remove the by-products. Another problem arises from the thickness of the photoresist, which is up to 5000-7000 .ANG. on average. That results in a high aspect ratio which makes it difficult to define the self-aligned contacts.